### University of Crete HEP Seminars

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Holographic Chern–Simons defects
**

Speaker: | Mitsutoshi Fujita |

Institution: | University of Kentucky |

Time: | Tuesday 18 October 2016, 14:00 |

Venue: | 2nd floor seminar room |

Abstract: | We study SU(N) Yang–Mills–Chern–Simons theory in the presence of defects that shift the Chern–Simons level from a holographic point of view by embedding the system in string theory. The model is a D3–D7 system in Type IIB string theory, whose gravity dual is given by the AdS soliton background with probe D7-branes attaching to the AdS boundary along the defects. We holographically renormalize the free energy of the defect system with sources, from which we obtain the correlation functions for certain operators naturally associated to these defects. We find interesting phase transitions when the separation of the defects as well as the temperature are varied. We also discuss some implications for the Fractional Quantum Hall Effect and for two-dimensional QCD. |

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A universal theory for fluid dynamics with explicitly broken boost
symmetries
**

Speaker: | Jelle Hartong |

Institution: | The Niels Bohr Institute, Copenhagen University |

Time: | Tuesday 7 February 2017, 14:15 |

Venue: | 2nd floor seminar room |

Abstract: | Theoretical investigations into the properties of strange metals suggest that these are described by effective field theories that are strongly coupled and that have non-relativistic scaling exponents. Such systems do not have boost invariance. In this talk I will discuss how to describe such theories in the hydrodynamic limit. More explicitly, I will first discuss an ideal gas of particles with dispersion relation w ~ k^z for any z. I will then describe the general thermodynamic properties of systems with no boost symmetries by introducing velocity as a chemical potential whose conjugate variable is momentum. I will then define perfect fluids and finally discuss first order corrections in the case of broken Galilean boost invariance. |

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Mixed Correlator 4D N=1 Superconformal Bootstrap
**

Speaker: | Andreas Stergiou |

Institution: | CERN |

Time: | Tuesday 21 February 2017, 14:15 |

Venue: | 2nd floor seminar room |

Abstract: | The numerical conformal bootstrap program has produced a wide range of impressive results concerning conformal field theories in various spacetime dimensions. In this talk I will focus on an application of this program to four-dimensional conformal theories with N=1 supersymmetry. In such theories a kink was found some time ago in the upper bound on the dimension of the first real scalar operator that appears in the operator product expansion of a chiral operator with its conjugate. Kinks signify isolated solutions to crossing equations, and are typically associated with specific conformal field theories. The nature of the putative theory at the N=1 kink remains mysterious. In this talk I will present numerical results concerning 4D N=1 theories using mixed correlation functions, and provide ample evidence that a special conformal field theory lives at the kink. |

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MOND cosmology
**

Speaker: | Richard Woodard |

Institution: | University of Florida |

Time: | Tuesday 14 March 2017, 14:15 |

Venue: | 2nd floor seminar room |

Abstract: | Milgrom's MOdified Newtonian Dynamics (MOND) provides a wonderful explanation for galactic structure, as shown by the striking recent work of McGaugh and collaborators (arXiv:1609.05917). However, MOND must be regarded as the weak field, static limit of some larger, relativistic field theory. It is this larger theory which controls MOND cosmology, and also the model's predictions for recently disturbed systems such as the Bullet Cluster. I report on a nonlocal, pure metric realization of MOND which was developed by Deffayet, Esposito-Farese and myself in arXiv:1405.0393. The model is based upon an algebraic function of a nonlocal scalar which is typically positive for gravitationally bound systems, but is typically negative for cosmological settings. Correctly reproducing MOND phenomenology for galaxies therefore determines how the algebraic function depends on positive arguments but does not constrain its dependence on negative arguments. I report on a recent determination (arXiv:1608.07858) of the negative branch which succeeds in enforcing the Lambda CDM expansion history, without dark matter, until very late redshifts (z < 0.088). This means that the model agrees with the usual predictions of Big Bang Nucleosynthesis and at least has the same cosmological background geometry as usual during Recombination. Interestingly, the expansion history deviates at very late times in such a way as to reduce the growing tension between inferences of the Hubble parameter based on data from large redshifts and inferences based on data from small redshifts. Because no more freedom exists in the model, its response to perturbations can now be studied to see if it agrees with the observed pattern of Doppler peaks in the Cosmic Microwave Radiation, and also if it is in rough agreement with structure formation. |